The present invention relates to a method and apparatus for imaging photographic negatives onto light-sensitive photoprint material. More particularly, the invention relates to both a conventional analog projection system for photographic negatives and a digital image projection system for index prints and other electronically generated images.
A device for producing prints from photographic negatives and for imaging index prints is disclosed in the European Patent Publication No. OS 0,308,967. In this case, a series of photographic images is projected onto photosensitive printing material. After printing the last image of the series, a mirror is mechanically pivoted into the light ray path of the integrated printing unit, and an index print is projected onto the same strip of photosensitive material. The index print is generated by a cathode ray tube (CRT). Additionally, the German Patent Application No. 196 23 835 discloses a photographic printing device wherein, after printing a series of photographic images, a light transmissive display unit, such as a liquid crystal display (LCD), is inserted into the printing light ray path. By means of this display unit, an index print is projected onto the light-sensitive photoprint material. In this case, the same light source is used for the index prints as for printing the series of images.
Switching over from one type of projection to the other requires much time in these known devices, so that printing output is slow. Additionally, adjustment of the folding mirror and of the LCD transmissive display unit is very expensive and requires costly pivoting mechanisms.
The photographic printer disclosed in the German Patent Publication No. 4,418,601 has two printing stations. These project regular prints and index prints onto the same strip of print material, acting consecutively and in offset fashion. The disadvantage of this arrangement is that two support platforms are necessary for the photoprint material. Also, the illumination areas onto which the regular prints and index prints are projected must be adjusted very exactly with respect to each other. A quite expensive additional procedure is required for this, in which the length of the photoprint material is monitored and controlled.
Therefore, a principal object of the present invention is to develop an appropriate method and device for imaging of photographic negatives onto light-sensitive photoprint material which makes possible the simple and reliable imaging of both analog and digital images onto this photoprint material. Printing speed is to be improved by a fast change-over between a digital image and an analog negative image projection.
This object, as well as other objects which will become apparent from the discussion that follows, are achieved, according to the present invention, by providing both a digital and an integrated (negative) image projection system, respectively, for which the light ray path of the integrated projection system is not influenced or changed in any way when the generated digital image is projected. This condition is satisfied and ensured by having the electronic image generator of the digital projection system disposed outside the light ray path of the integrated image projection system. The digital projection system is so designed and constructed that it projects the digital images onto the photoprint material on the same platform as does the integrated image projection system. In this way, a switch can be made between digital and integrated (negative) images without having to move mechanical components.
Thus, for example, in a photographic printing device, immediately after projection of a series of photographic images onto the light-sensitive photoprint material, the electronically generated images for the index prints can be projected onto the same printing paper platform. Such an arrangement also offers the option of projecting electronically generated image data, such as lines of type, directly and simultaneously with the analog images onto the photoprint material. A further option is to scan in the analog pictures, and then modify the electronic image data. Thus, for example, it is possible to electronically mask the scanned in images and then project them onto the photoprint material via the digital protection system. Alternatively or in addition, it is possible to electronically change the contrast or coloration of the images. With modification of the digital data, many other types of changes are possible.
According to the invention, the digital image can be formed by means of a light modulator that can be driven by a control device in a pixel mode. The light modulator can be either reflecting or transmissive. DMDs (digital micromirror devices as are described, for example, in the European Patent Publication No. OS 0,738,910), LCDs (liquid crystal displays), FLCDs (ferroelectric liquid crystal displays) or PLZTs (piezo-electric lithium, zirconium titanate displays), as well as any other pixel-controllable light modulators, can be used. DMDs are particularly advantageous, because they are very bright and can be switched very quickly. This reduces the required illumination time and thus makes possible rapid printing. Owing to the small light loss when DMDs are used, LEDs can be used for the illumination (light source). These have the advantage that, like DMDs, they can be switched rapidly. They can be quickly switched off between illuminations to avoid an incidence of stray light. No additional sealing apparatus is therefore required as must be used with light sources that switch more slowly. Additionally, their long service life makes LEDs particularly advantageous light sources.
If, in contrast, transmissive light modulators are used, then it is more advantageous to use higher-intensity light sources such as halogen or incandescent lamps, since transmissive light modulators absorb much of the light.
A further option for configuring the invention makes provision to use a CRT or an LED array as an electronic image generator.
The image that is generated by the electronic image generator is projected by a lens onto the light-sensitive photoprint material. Normally the image generator and the light-sensitive material that form the object and image plane are parallel to each other, to ensure a sharp, undistorted image. Only those light rays are imaged which go through a small peripheral area of the lens. The optical axis of the lens is not used, as can be seen from FIG. 1. To utilize the optical axis of the lens, the lens must be placed aslant to the image plane. The electronic image generator is then so placed that the Scheimpflug condition is met, so that a sharp image is produced on the photoprint material. To maintain an undistorted image with this arrangement, the digital pattern must be pre-distorted so that the distortion is compensated by imaging with the lens.
This pre-distortion can be effected in such a way that the electronic image data are modified in a computer to create an appropriately pre-distorted image using the control device on the electronic image generator.
Correction of the distortion can also be effected optically, as is illustrated in FIG. 3. This is done by inserting an additional imaging optical system in front of the lens. This generates an appropriately pre-distorted intermediate image, so that when the next imaging is done, a reproduction of the pattern that is again undistorted is produced by the lens. Either a virtual or a real intermediate image can be generated on a ground-glass plate. Condensing lenses that are additionally brought into the light ray path enhance the brightness.
Another possibility to use the optical axis of the lens in projecting the digital image is to reflect the image, using a partially transmitting (half-silvered) mirror that is in the light ray path of the integrated (negative) projection system, onto the light-sensitive photoprint material.
For a full understanding of the present invention, reference should now be made to the following detailed description of the preferred embodiments of the invention as illustrated in the accompanying drawings.